Clinically, atrial arrhythmias are one of the most frequently encountered of the cardiac arrhythmias. Annually, more than 500,000 individuals are diagnosed with atrial arrhythmias, including atrial fibrillation, flutter and tachycardia. While these conditions are not immediately life-threatening, they can lead to serious health risks if left untreated. These include the increased potential for developing chronic fibrillation, embolic strokes and for transferring the aberrant atrial electrical signals to the ventricles, which can result in ventricular tachycardia and/or ventricular fibrillation.
Treating atrial fibrillation has traditionally involved the use of antiarrhythmic agents. However, patients who have experienced only one episode or infrequent paroxysmal episodes of atrial fibrillation may not want the inconvenience of daily medication and follow-up. Alternatively, patients with recurrent episodes are at the highest risk for a thromboembolism and often are candidates for maintenance antiarrhythmic and anticoagulation therapies. This long-term therapy, however, can have potential drawbacks as chronic use of some antiarrhythmic agents may have toxic side effects. As a result, effective alternatives to chronic pharmacological treatment have been sought.
Implantable atrial cardioverter/defibrillators are a potential solution to acutely treat atrial fibrillation. The implantable atrial cardioverter/defibrillators sense and analyze atrial cardiac signals to detect the occurrence of an atrial arrhythmia. Once an atrial arrhythmia is detected, the device can deliver a low energy discharge of cardioverting/defibrillating electrical energy across the atria of the heart in an attempt to terminate the arrhythmia and to restore normal sinus rhythm. In designing these devices, investigators have also proposed synchronizing the delivery of the atrial defibrillation pulse to the sinus rhythm of the ventricles so as to avoid triggering a ventricular arrhythmia. While these suggested methods attempt to prevent inducing a ventricular arrhythmia, there remains the possibility of inducing a ventricular tachyarrhythmia or a ventricular fibrillation by inadvertently delivering a cardioverting/defibrillating electrical energy pulse during a T-wave that resulted from an aberrant ventricular contraction. Therefore, a need still exists for a system to safely and reliably treat a supraventricular arrhythmia.